Method for making hard metal compositions



Patented July 11, 1933 UNITED ROBERT PALMER, OF

NISKAYUNA, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COM- IANY, ACORPORATION OF NEW YORK METHOD FOR MAKING HARD METAL COMPOSITIONS NoDrawing. Original application filed October 8, 1930, filed October 14,1931.

This application is a division of my copending application Serial No.487,371, filed October 8, 1930.

The present invention relates to hard metal compositions andparticularly to a method for making hard metal compositions which aresuitable for use in electrical apparatus.

It is a specific object of the present invention to provide a method formanufacturing pressure Welding electrodes. Other objects of theinvention will appear hereinafter.

In carrying out my invention, I impregnate a formed, porous and partlysintered hard metal carbide mass, such as tungsten carbide, with arelatively soft metal which is an electrical conductor and which willwet tungsten carbide, for example copper or an equivalent metal oralloy. Tungsten carbide has no ductility and has a rather low degree ofelectrical conductivity, whereas in electrical apparatus such aspressure Welding tips or rods, it is desirable to have a certain amountof ductility as well as a high degree of electrical conductivity. Theaddition of copper to the carbide provides the latter with asatisfactory degree of ductility and conductivity. Although copper doesnot alloy with carbon and only alloys to a slight "degree with tungsten,I have found that molten copper will wet tungsten carbide whether thelatter is under-saturated or slightly supersaturated with carbon 85 andform a very strong bond with it.

The carbide employed in the present invention should be quite spongy orporous in order to be able to take up a suitable quantity of copper andthereby provide a ductile product having good electrical conductivity. Acarbide of this character may be obtained by mixing tungsten carbide insuitable proportions with an agglutinant or adhesive binder material anda liquid as described in the copending application of Louis Navias,Serial No. 319,184, filed November 13, 1928, and entitled Plasticcompositions. The binder material described in the Navias applicationmay be prepared 5 by mixing at room temperature about Serial No.487,371. Divided and this application Serial No. 568,878.

grams of wheat flour with 300 grams of water and heating themixtureuntil a pasty gel is formed. To this mass an electrolyte such asammonia, sodium or potassium hydroxide or acetic acid is added. In thecase of ammonia a 25 gram concentrated solution is employed. Althoughthe ammonia is preferred as a stabilizing agent for some purposes as itis volatile and leaves no residue which may combine chemically with themain ingredients, a suitable amount of a 20% sodium hydroxide solutionmay be employed with satisfactory results when such a combination is notobjectionable. About 10% by weight of flour or starch paste, prepared asindicated above, is mixed with about 90% tungsten carbide, and themixture shaped either by molding or extrusion through a suitable die.The shaped product thus formed is heated or partly sintered in ahydrogen atmosphere at a temperature of about 1100 C. The partialsintering burns out thefiour or starch paste binder and at the same timegives the formed carbide a certain degree of rigidity so that it may behandled easily without breakage. Lower temperatures than 1100 C. may beemployed if desired but with lower temperatures the heat has to beapplied to the product for a longer period of time in order to burn outcompletely the binder material.

When the binder material has been removed from the carbide the latter isquite and the tungsten carbide particles are partly bonded together bydirect contact at their corners or edges. The porous mass is now placedin an open carbon boat containing pieces of copper and heated in ahydrogen atmosphere to a temperature of about 1150 C. to 1250 C. At thistemperature, the copper is in a molten condition and runs into the poresof the carbide .mass. If. sufficient copper is employed the pores willbe completely filled and the carbide particles substantially completelybonded by the molten copper.

The amount of copper contained in the finished product may varyconsiderably. As an example, I have found that satisfactory weldingelectrodes may be made porous or spongy from a composition consisting ofabout 20% copper with the remainder tungsten carbide. Such an electrodeis strong, solid, a satisfactory electrical conductor, is capable ofresisting deformation when subjected to a relatively heavy pressure andhas a low-contact resistance.

Although my invention has been described in connection with electricalapparatus such as pressure Welding electrodes, it is not limited to suchuse. A tungsten carbide copper composition, besides being a goodelectrical conductor has also the property of resisting abrasion and maytherefore be used as a-burnishing wheel if desired. When rubbed overhard steel or softer metal such as brass, the copper impregnated carbideproduces a burnished surface on such metals which is uniformly smoothand adapted to receive oil lubrication when employed as a bearingsurface. Also, if desired, the hard metal composition may be employedfor switch contacts, trolley wheels, contact shoes for trolley wires andsteel rolls, bearing boxes and journals and bearing rolls and the like.

Silver'wets tungsten carbide in the same manner as copper and, ifdesired, may be substituted for copper in my improved welding electrode,or in the other uses indicated above. While I ordinarily prefer copperrather than silver as the bonding metal for tungsten carbide, I preferto employ silver as the bonding metal when the .hard metal compositionis employed as a switch or regulator contact.

What. I claim as new and desire to secure by Letters Patent of theUnited States, 1s:

1. The method of manufacturing a metal structure which comprises mixinga hard metal carbide with a starchy binder material, applying pressureto the mixture to thereby shape it, heating the shaped mixture therebyto expel said binder and partly sinter said carbide, thereaftersintering the carbide at a temperature above 1100 C. and impregnating itwith a metal which is a good electrical conductor.

2. The method of manufacturing a strong pressure-resisting metalstructure which comprises mixing tungsten carbide particles with astarchy binder material, applying pressure to the mixture to therebyshape it, heating the mixture to expel the binder material and form aporous carbide structure, thereafter sintering the carbide at anelevated temperature and impregnating it with a metal which is a goodelectrical conductor. 3. The method of making a'strongpressure-resisting metal structure which comprises mixing pulverizedtungsten carbide with an organic binder material, applying pressure tothe mixture to thereby shape it, heating the shaped mixture to anelevated temperature to expel said binder and impregnating the carbidewith a relatively soft metal which is a good electrical conductor.

4. The method of making a strong, pressure-resisting metal structurewhich comprises mixing pulverized tungsten carbide with an organicbinder material and a liquid, applying pressure to the mixture tothereby shape it, heating the shaped mixture to an elevated temperatureto expel the binder material and impregnating the carbide with arelatively soft electrical-1y conducting metal.

5. The method of making a welding rod which comprises mixing particlesof tungsten-carbide with an organic binder and a liquid, extruding themixture, heating the extruded mixture to an elevated temperature toexpel the binder material and impregnating the carbide in a hydrogenatmosphere with copper.

6. The method of making a pressure welding elect-rode which comprisesmixing,

my hand.

ROBERT PALMER.

